GPS World, May 2016

WATCH MARKET MAY 2016 WWW GPSWORLD COM GPS WORLD 37 UAV 2 2 TRANSPORTATION Figure 3 Components of a V2X system Looking at the components of an over the air OTA V2X basic safety message BSM this includes a UTC based time marker WGS84 based position and an estimated position error all critical data that primarily depend on GNSS RTCM formatted data may also be sent as optional attachments A BSM like personal safety message PSM is also defined for pedestrians with V2X enabled devices As per current Minimum Performance Requirements MPR a UTC time source with better than 1 millisecond accuracy is required in a V2X device While almost all current prototypes use GNSS as source of time others such as NTP may also be used Accurate time reference is a critical prerequisite for basic DSRC functionality MPR requires time marked position estimates with 2D and elevation accuracy of 15 and 3 meters or better 1 sigma under open sky conditions The automotive industry has opted to define open sky as unobstructed sky view above 5 degree elevation with seven or more satellites visible with HDOP and VDOP limits The industry expectation is to use this criteria to select GNSS devices that could eventually support lane level applications better than 15 meter accuracy MPR does not put any requirements on the accuracy of the position error estimate in the BSM It does require that a vehicle stop transmitting BSM whenever the aforementioned time and position accuracy requirements are not met This implies that a V2X enabled vehicle may disappear from the V2X view of others in a dense urban canyon or similar environments leaving at least two questions for system designers from a GNSS perspective alone First how to reliably declare that the system cannot meet time and position accuracy requirements and second how to deal with the vehicle itself and other V2X entities that may cease to function or broadcast due to GNSS or other limitations V2X systems are assumed to include inertial and vehicle sensor integration Road Ahead Starting in 2017 connected vehicle pilots CVP in New York Tampa Florida and Wyoming will be the next major milestone for V2X These deployments will be limited to commercial fleets taxis public transit city road crews and delivery trucks and some limited roaduser categories Among the automotive OEMs Toyota was the first to offer V2X based driver assistance technology as ITS Connect in Japan in 2015 General Motors is the first to announce a V2X technology offering in a passenger vehicle in the U S with an initial rollout in select 2017 models The first phase of V2X deployments will only provide driver assistance information while subsequent iterations are expected to bring in safetyfocused functions leading to control capabilities There is a growing interest in the cellular industry to support V2X like communication in an upcoming release of the 3GPP standards commonly referenced as 5G This would enable low latency peer to peer communication with the advantage of an existing device provisioning authentication infrastructure something that needs to be built up for DSRC However 5G is still a concept and judging by the lifecycle of LTE a 5G deployment will take several years to start and several more years to fully deploy while still leaving some rural areas with legacy technology A framework to manage commercial traffic vs likely free safety traffic will also be required These raise the question as to how 5G alone can support vehicle safety applications nationwide The FCC has recently proposed a rule to potentially open up the DSRC band for unlicensed Wi Fi devices provided Wi Fi users do not interfere with the primary safety use Automotive and wireless industry and other stakeholders are investigating the feasibility of possible coexistence in the future Among the proposed solutions are the rechannelization of DSRC to use a smaller bandwidth and a mechanism for Wi Fi devices to Detect and Vacate the DSRC band when a safety user is detected From a technology point of view V2X has reached a significant milestone with R D in various technology areas converging and critical standards being adopted recently With Toyota V2X offering in Japan and GM V2X commitment in the U S customers will have V2X as an option this year further proof that V2X will be on the roads soon However significant further work is needed to address the GNSS accuracy and reliability needed for next generation systems and to address GNSS specific vulnerabilities such as jamming or spoofing The New York CVP which includes deep urban canyons will probably be a great opportunity for GNSS and V2X communicates to work together on some of these limitations

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